1. Field of the Invention
The present invention relates to a driving apparatus including a driving device that drives or moves an object such as a carriage, a linear encoder, and a control device or portion that controls, based on an output of the linear encoder the driving device to move the object.
2. Discussion of Related Art
There has been known a linear driving apparatus which includes a linear motor, or a combination of a rotary motor and a converting device that converts a rotary driving force of the rotary motor into a linear motion, and which linearly drives or moves an object by utilizing the linear motion. Generally, this sort of linear driving apparatus performs a so-called feedback control in which a position or a velocity of the object is detected and the motor, or the linear movement of the object is controlled based on the detected result.
A serial-type printer such as an ink-jet printer employs the above-indicated linear driving apparatus that performs the feedback control. The serial-type printer includes a carriage that carries a printing or recording head, and reciprocates the carriage in a main scan direction perpendicular to a sub-scan direction in which a recording sheet is fed, so as to record an image on the sheet.
The serial-type printer additionally includes a linear encoder that detects, during an image recording operation of the recording head, a position or a velocity of the carriage so as to control the velocity of the carriage to a constant value. The feedback control of the carriage is performed based on a detection signal outputted by the linear encoder.
There have been known various sorts of linear encoders each of which detects a position or a velocity of a carriage; such as an optical linear encoder or a magnetic linear encoder. Generally, each sort of linear encoder includes a linear scale having a plurality of detectable portions arranged at a regular interval of distance; and a detector that reads or detects each of the detectable portions in a manner specific to said each sort. For example, in the case of the optical linear encoder, the linear scale thereof has, as the detectable portions, a plurality of slits, or a plurality of reflectors, that are arranged at a regular interval of distance; and in the case of the magnetic linear encoder, the linear scale thereof has, as the detectable portions, a plurality of north (N) poles and a plurality of south (S) poles that are alternately arranged at a regular interval of distance. When the object such as the carriage is moved, the detectable portions of the linear scale are read by the optical or magnetic detector, so as to detect an amount of movement of the object.
The serial-type printer is required to carry out accurately various operations such as the image recording operation. To this end, the serial-type printer needs to detect not only the amount of movement of the object but a position of the same relative to the linear driving apparatus, e.g., a housing or a frame of the printer. Generally, the printer carries out, at an appropriate timing, a so-called origin or home-position detecting operation to detect an origin or a home position (i.e., a reference position) of the carriage, and determines, based on the detected home position, a current position of the carriage. This serial-type printer is disclosed by, e.g., Japanese Patent Application Publication No. 2004-25549.
The home-position detecting operation is carried out such that the carriage is moved to engage or contact a side frame of the printer and is physically locked or stopped by the same. FIG. 19 shows a graph representing respective time-wise changes of an actual velocity of the object i.e., the carriage), a detected (i.e., calculated) velocity of the carriage, detected (i.e., calculated) based on the encoder signal outputted by the linear encoder, and a motor driving or operating amount (i.e., an electric current supplied to the motor), each in the home-position detecting operation.
As shown in FIG. 19, in a steady state after the start of the home-position detecting operation and before a time point, A, i.e., 4 seconds after the start, the carriage (the object) is moved at a substantially constant velocity (i.e., 5 inches/sec.) and the motor operating amount is kept at a substantially constant value. At the time point A, the carriage impacts on the side frame, and the movement of the carriage is stopped by the frame. Thus, the detected velocity of the carriage is lowered to zero and accordingly the motor operating amount is increased to an upper limit amount (i.e., 25, shown in FIG. 19), i.e., is saturated, so as to move the carriage at the target velocity. If this saturated state continues for a predetermined time period, B (e.g., 0.5 second), then it is judged that the carriage has impacted on the side frame and the current position of the carriage, indicated by a number counted based on the encoder signal, is determined as the home position (the origin) of the carriage, that is, the counted number is reset to zero.